//           https://www.nowcoder.com/questionTerminal/953b74ca5c4d44bb91f39ac4ddea0fee




#include <iostream>
using namespace std;

int dp[21] = { 1, 1, 2 };

int main()
{
    int n;
    cin >> n;

    for (int i = 3; i <= n; i++)
        for (int j = 0; j < i; j++)
            dp[i] = dp[i] + dp[j];

    cout << dp[n];
    return 0;
}